Enzymatic Synthesis Of Monoacyl Maltitols And Their Propetries

Maltitol is a disaccharide, obtained from the hydrogenization of maltose. Althoughseveral properties are similar with those of sucrose such as solubility in water and sweeteningpotency, maltitol has the ability of prophylaxis decayed tooth and diabetes mellitus and lowerenergy value, higher stability on the thermal than those of sucrose. Matitol is becomingincreasingly popular. However, maltitol was limited in the use of food due to its expensivecosts and low lipophilicity. Maltitol esters, the derivative with high added value of maltitol,would extend maltitol applicable field. Fatty acid was condensed with maltitol usingimmobilized enzyme in a non-aqueous phase to synthesize maltitol fatty acid esters which hadgood surfactivity and antibiotic ability. We also studied its properties to guide the productionand application of maltitol esters and widen the application of maltitol.First, solubility of maltitol and esterification ratio of monolaurate maltitol wereconsidered to select solvents and enzymes. It was found that the tertiary amylalcohol/DMSO=4:1and Novozym435were used as solvent and lipase for the experiment,respectively. The highest concentration of monolaurate maltitol （42.7mmol/L） was achievedin the optimized reaction conditions: molar ratio of lauric acid to maltitol was4:1, lipasecontent was10g/L, maltitol concentration was100mmol/L,60g/L4molecular sievesafter12h, condensation for72h at50℃. Maltitol laurate was separated and purified by silicagel column and semi-preparation high performance liquid chromatography （HPLC）. Thepurified products were identified as6-O-lauroyl maltitol and6’-O-lauroyl maltitol by MS,FT-IR and13C NMR.HLB values of maltitol monoesters were from11.25to14.6, and could be used for thepreparation of nonionic O/W microemulsions. Surface tension curves were measured usingthe Small Wilhelmy-Plate method for monoacyl maltitol at30⁶0℃, respectively. Thecritical micelle concentrations （CMC）, surface tension at the CMC （γCMC）, Γmaxand Aminofthese amphiphilic compounds were studied. The results showed that the surface tension ofmonoacyl maltitols were35.13²6.45mN/m, CMC of monoacyl maltitols were10^-410^-6mol/L. The surface tension and CMC of monoacyl maltitols were slightly decreased with theincrease of temperature. Compared with other sugar esters, monoacyl maltitols had lowersurface tension and CMC. The thermodynamic parameters were obtained from the surfacetension curves and formulas. We knew that micelle formation was an entropy-driven,endothermic and spontaneous process.The minimum inhibitory concentration （MIC） and the inhibition ability of monoacylmaltitol against bacteria and yeast at different concentrations were investigated. Theinfluences of different hydrophilic group and hydrophobic groups on the antimicrobial abilityof fatty acids esters were studied. It was found that monoacyl maltitols were efficient toinhibit microorganism. The inhibition ability of monolaurate maltitol was similar to othersugar esters, particularly against Streptococcus mutans. The MIC of monolaurate maltitolagainst Eschericheae coli, Bacillus subtilis and Streptococcus mutans were2.0mg/mL,0.5mg/mL,0.25mg/mL. The inhibition against Yarrowia lipolytica was relatively weak. Among the four monomaltitol esters, the antibiotic ability of monolaurate was strongest,monocaprylate and monooleate came second and monostearate had weaker antibacterialaction.